Dyeing of filament nylon fabrics is conventionally performed by batch processes or on a jig, which may be considered a semi-continuous process. Attempts to dye filament nylon fabrics by conventional continuous processes result in intolerable variations in color from place to place, from side to side, from front to back, or from end to end of the fabric. The problems of non-uniformity are sufficiently severe so that filament nylon fabrics are not dyed continuously on a commercial basis.
The process of this invention, which may be conducted on a continuous dyeing range, employs a dye assistant system to effectively and uniformly dye filament nylon fabrics and low-denier, high-tenacity continuous filament fabrics. This continuous process uses an aqueous-based, homogeneous system and produces uniform, non-striated, dyed filament nylon with exceptional fiber bunder penetration. The process is more economical than conventional batch dyeing apparatus and uses commercially available range equipment. The process is continuous and the dyed fabric is of a more uniform quality, including a non-striated appearance with well-penetrated yarn bundles, from end to end and piece to piece as compared with fabrics dyed using the conventional batch procedure. The process of the invention successfully dyes normal tenacity continuous filament nylon 6 and nylon 66 as well as high tenacity nylon fabrics made from nylon yarns with a low denier per filament, i.e., a low filament diameter.
As used in this disclosure, the term high-tenacity nylon refers to fibeers of a high tensile strength nylon yarn having a low filament diameter spun from poly(hexamethyleneadipamide), or 6,6 nylon, which has a draw ratio of at least 4.0, and preferably in the range of 4.6 to 5.1 Such fibers are disclosed in U.S. Pat. No. 3,433,008 to Gage, and are currently commercially available from various sources including Cordura.RTM. from DuPont, Wilmington, Del. These fibers are used to make fabrics which are in turn formed into long-wearing, abrasion-resistant articles of clothing, suitcase and handbag material, antiballistic clothing and protective devices and similar articles.
The currently preferred Cordura.RTM. product contains approximately twice as many amino end-groups as conventional nylon. The presence of these end-groups favours undesirable ring dyeing of the fabric, and makes uniform dyeing and complete penetration of the yarn bundle difficult in a continuous process. Ballistic nylons and other high-tenacity nylon products may not contain an unusually high content of amine end-groups as does Cordura.RTM., but they are also easily dyed by the process of this invention if their denier per filament is low.